LITTORAL PROCESSES IN A PROGRADING COAST: THE CASE STUDY OF THE ATLANTIC OCEAN COAST OF URUGUAY

Abstract

The Atlantic Ocean coast of Uruguay extends from Punta del Este outer limit of the Rio de la Plata Estuary, to the Brazilian border, over 220 kms. This case study applies to a homogeneous coastal stretch of 80 kms long, north of Punta del Este. The main coastal features are three littoral lagoons, Jose Ignacio, Garzon and Rocha, whose mouths open and close by natural or antropic actions every year. The coastline is formed by 1-2 mm coarse sand on highly reflective beaches. Beach berm is overwashed by the SE storm waves. Landward there is a dune system. This beach-dune structure is approximately 100 m wide. At least three similar morphological structures may be landward identified, which were developed during a period of time when the sea level was about 5 m higher than today's sea level (approximately 5000 years BP). 14C technique applied to chalk samples shows a relative decrease of the sea level in the last 5000 years. Furthermore, gravimetric data shows that there is an anomaly, which supports the existence of an isostatic rise of the continental shelf. As a result, the Atlantic Ocean Coast of Uruguay is prograding. The beach coarse material is provided by the wave action from the continental shelf, while the fine dune material seems to be obtained from the erosion of the land weathered granite.